arXiv subjects

Satoshi Iso

Publications and source records attributed to Satoshi Iso.

At least 55 records · Page 3Linked to original sources

arXiv2015

Revolving D-branes and Spontaneous Gauge Symmetry Breaking

We propose a new mechanism of spontaneous gauge symmetry breaking in the world-volume theory of revolving D-branes around a fixed point of orbifolds. In this paper, we consider a simple model of the T6/Z3 orbifold on which we put D3-branes, D7-branes and their anti-branes. The configuration breaks supersymmetry, but the R-R tadpole cancellation conditions are satisfied. A set of three D3-branes at an orbifold fixed point can separate from the point, but when they move perpendicular to the anti-D7-branes put on the fixed point, they are forced to be pulled back due to an attractive interaction between the D3 and anti-D7 branes. In order to stabilize the separation of the D3-branes at nonzero distance, we consider revolution of the D3-branes around the fixed point. Then the gauge symmetry on D3-branes is spontaneously broken, and the rank of the gauge group is reduced. The distance can be set at our will by appropriately choosing the angular momentum of the revolving D3-branes, which should be determined by the initial condition of the cosmological evolution of D-brane configurations. The distance corresponds to the vacuum expectation values of brane moduli fields in the world-volume theory and, if it is written as M/Ms^2 in terms of the string scale Ms, the scale of gauge symmetry breaking is given by M. Angular momentum conservation of revolving D3-branes assures the stability of the scale M against Ms.

hep-ph↗

arXiv2015

TeV Scale B-L model with a flat Higgs potential at the Planck scale -- in view of the hierarchy problem

The recent discovery of the Higgs-like particle at around 126 GeV has given us a big hint towards the origin of the Higgs potential. Especially the running quartic coupling vanishes near the Planck scale, which indicates a possible link between the physics in the electroweak and the Planck scales. Motivated by this and the hierarchy problem, we investigate a possibility that the Higgs has a flat potential at the Planck scale. In particular, we study the RG analysis of the B-L extension of the standard model with a classical conformality. The B-L symmetry is radiatively broken at the TeV scale via the Coleman-Weinberg mechanism. The electroweak symmetry breaking is triggered by a radiatively generated scalar mixing so that its scale 246 GeV is dynamically related with the B-L breaking scale at TeV. The Higgs boson mass is given at the border of the stability bound,which is lowered by a few GeV from the SM by the effect of the B-L gauge interaction.

hep-ph↗

arXiv2015

Small Field Coleman-Weinberg Inflation driven by Fermion Condensate

We revisit the small field Coleman-Weinberg (CW) inflation, which has the following two problems. First, the smallness of the slow roll parameter $ε$ requires the inflation scale to be very low. Second, the spectral index $n_s \approx1+2 η$ tends to become smaller compared to the observed value. In this letter, we consider two possible effects on the dynamics of inflation: radiatively generated non-minimal coupling to gravity $ξϕ^2 {\cal R}$ and condensation of fermions coupled to the inflaton as $ϕ\barψψ$. We show that the fermion condenate can solve the above problems.

hep-ph↗

arXiv2014

Evolution of vacuum fluctuations generated during and before inflation

We calculate the time evolution of the expectation value of the energy-momentum tensor for a minimally-coupled massless scalar field in cosmological spacetimes, with an application to dark energy in mind. We first study the evolution from inflation until the present, fixing the Bunch-Davies initial condition. The energy density of a quantum field evolves as $ρ\sim 3(H_I H)^2 /32 π^2 $ in the matter-dominated (MD) period, where $H_I$ and $H$ are the Hubble parameters during inflation and at each moment. Its equation of state, $w=ρ/p$, changes from a negative value to $w=1/3$ in the radiation-dominated period, and from $1/3$ to $w=0$ in the MD period. We then consider possible effects of a Planckian universe, which may have existed before inflation, by assuming there was another inflation with the Hubble parameter $H_P (> H_I)$. In this case, modes with wavelengths longer than the current horizon radius are mainly amplified, and the energy density of a quantum field grows with time as $ρ\sim (a/a_0)(H_P H)^2/32$ in the MD period, where $a$ and $a_0$ are the scale factors at each time and at present. Hence, if $H_P$ is of the order of the Planck scale $M_P$, $ρ$ becomes comparable to the critical density $3(M_P H)^2$ at the present time. The contribution to $ρ$ from the long wavelength fluctuations generated before the ordinary inflation has $w=-1/3$ in the free field approximation. We mention a possibility that interactions further amplify the energy density and change the equation of state.

hep-th↗

arXiv2014

Coherent Flavour Oscillation and CP Violating Parameter in Thermal Resonant Leptogenesis

Solving the Kadanoff-Baym (KB) equations in a different method from our previous analysis, we obtain the CP violating parameter $\varepsilon$ in the thermal resonant leptogenesis without assuming smallness of the off-diagonal Yukawa couplings. For that purpose, we first derive a kinetic equation for density matrix of RH neutrinos with almost degenerate masses $M_i \ (i=1,2) \sim M$. If the deviation from thermal equilibrium is small, the differential equation is reduced to a linear algebraic equation and the density matrix can be solved explicitly in terms of the time variation of (local) equilibrium distribution function. The obtained CP-violating parameter $\varepsilon_i$ is proportional to an enhancement factor $(M^{2}_{i}-M^{2}_{j}) M_i Γ_j/ ((M^{2}_{i}-M^{2}_{j})^2 +R_{ij}^2)$ with a regulator $R_{ij}=M (Γ_i + Γ_j)$, consistent with the previous analysis. The decay width can be determined systematically by the 1PI self-energy of the RH neutrinos in the 2PI formalism.

hep-ph↗

arXiv2014

Radiative Symmetry Breaking from Flat Potential in various U(1)' models

We investigate a radiative electroweak gauge symmetry breaking scenario via the Coleman-Weinberg mechanism starting from a completely flat Higgs potential at the Planck scale ("flatland scenario"). In our previous paper, we showed that the flatland scenario is possible only when an inequality K<1 among the coefficients of the beta functions is satisfied. In this paper, we calculate the number K in various models with an extra U(1) gauge sector in addition to the SM particles. We also show the renormalization group (RG) behaviors of a couple of the models as examples.

hep-ph↗

arXiv2014

Kadanoff-Baym approach to the thermal resonant leptogenesis

Using the non-equilibrium Green function method (Kadanoff-Baym equations) in the expanding universe, we investigate evolution of the lepton number asymmetry when the right-handed (RH) neutrinos have almost degenerate masses $|M_i^2-M_j^2| \ll M_i^2$. The resonantly enhanced $CP$-violating parameter $\varepsilon_i$ associated with the decay of the RH neutrino $N_i$ is obtained. It is proportional to an enhancement factor $(M_i^2-M_j^2) M_i Γ_j/ ((M_i^2-M_j^2)^2 +R_{ij}^2)$ with the regulator $R_{ij}=M_i Γ_i+M_j Γ_j$. The result is consistent with the previous result obtained by Garny et al., in a constant background with an out-of-equilibrium initial state. We discuss the origin of such a regulator, and why it is not like $R_{ij}=M_i Γ_i-M_j Γ_j$.

hep-ph↗

arXiv2014

Radiative symmetry breaking at the Fermi scale and flat potential at the Planck scale

We investigate a possibility of the "flatland scenario", in which the electroweak gauge symmetry is radiatively broken via the Coleman-Weinberg mechanism starting from a completely flat Higgs potential at the Planck scale. We show that the flatland scenario is realizable only when an inequality K<1 among the coefficients of the beta-functions is satisfied. We show several models satisfying the condition.

hep-ph↗

arXiv2013

What can we learn from the 126 GeV Higgs boson for the Planck scale physics ? - Hierarchy problem and the stability of the vacuum -

The discovery of the Higgs particle at around 126 GeV has given us a big hint towards the origin of the Higgs potential. The running quartic self-coupling decreases and crosses zero somewhere in the very high energy scale. It is usually considered as a signal of the instability of the standard model (SM) vacuum, but it can also indicate a link between the physics in the electroweak scale and the Planck scale. Furthermore, the LHC experiments as well as the flavor physics experiments give strong constraints on the physics beyond the SM. It urges us to reconsider the widely taken approach to the physics beyond the SM (BSM), namely the approach based on the gauge unification below the Planck scale and the resulting hierarchy problem. Motivated by the recent experiments, we first revisit the hierarchy problem and consider an alternative appoach based on a classical conformality of the SM without the Higgs mass term. In this talk, I review our recent proposal of a B-L extension of the SM with a flat Higgs potential at the Planck scale. This model can be an alternative solution to the hierarchy problem as well as being phenomenologically viable to explain the neutrino oscillations and the baryon asymmetry of the universe. With an assumption that the Higgs has a flat potential at the Planck scale, we show that the B-L symmetry is radiatively broken at the TeV scale via the Coleman-Weinberg mechanism, and it triggers the electroweak symmetry breaking through a radiatively generated scalar mixing. The ratio of these two breaking scales is dynamically determined by the B-L gauge coupling.

hep-ph↗

arXiv2012

The Einstein equation of state as the Clausius relation with an entropy production

We give a modified derivation of the Einstein equation of state by considering the Clausius relation $TδS-δN =δQ$ on a null hypersurface with a non-vanishing expansion ($θ\neq 0$), i.e. not in the equilibrium. The derivation corresponds to choosing a specific observer to the hypersurface, and such a generalization gives a hint how we can improve the original derivation by Jacobson. We also give an interpretation of the thermodynamic relation based on the Noether charge method.

gr-qc↗

arXiv2012

Radiation Reaction by Massive Particles and Its Non-Analytic Behavior

We derive a massive analog of the ALD (Abraham, Lorentz and Dirac) equation, i.e., the equation of motion of a relativistic charged particle with a radiation reaction term induced by emissions of massive fields. We show that the radiation reaction term has a non-analytic behavior as a function of the mass M of the radiation field and both expansions with respect of M and 1/M are generally invalid. Hence the massive ALD equation cannot be written as a local equation with derivative expansions. We especially investigate the radiation reaction in three specific motions, uniform acceleration, a circular motion and a scattering process.

hep-th↗

arXiv2012

Revisiting the Naturalness Problem -- Who is afraid of quadratic divergences? --

It is widely believed that quadratic divergences severely restrict natural constructions of particle physics models beyond the standard model (SM). Supersymmetry provides a beautiful solution, but the recent LHC experiments have excluded large parameter regions of supersymmetric extensions of the SM. It will now be important to reconsider whether we have been misinterpreting the quadratic divergences in field theories. In this paper, we revisit the problem from the viewpoint of the Wilsonian renormalization group and argue that quadratic divergences, which can always be absorbed into a position of the critical surface, should be simply subtracted in model constructions. Such a picture gives another justification to the argument that the scale invariance of the SM, except for the soft-breaking terms, is an alternative solution to the naturalness problem. It also largely broadens possibilities of model constructions beyond the SM since we just need to take care of logarithmic divergences, which cause mixings of various physical scales and runnings of couplings.

hep-ph↗

arXiv2011

Stochastic Analysis of an Accelerated Charged Particle -Transverse Fluctuations-

An accelerated particle sees the Minkowski vacuum as thermally excited, and the particle moves stochastically due to an interaction with the thermal bath. This interaction fluctuates the particle's transverse momenta like the Brownian motion in a heat bath. Because of this fluctuating motion, it has been discussed that the accelerated charged particle emits extra radiation (the Unruh radiation) in addition to the classical Larmor radiation, and experiments are under planning to detect such radiation by using ultrahigh intensity lasers constructed in near future. There are, however, counterarguments that the radiation is canceled by an interference effect between the vacuum fluctuation and the fluctuating motion. In fact, in the case of an internal detector where the Heisenberg equation of motion can be solved exactly, there is no additional radiation after the thermalization is completed. In this paper, we revisit the issue in the case of an accelerated charged particle in the scalar-field analog of QED. We prove the equipartition theorem of transverse momenta by investigating a stochastic motion of the particle, and show that the Unruh radiation is partially canceled by an interference effect.

hep-th↗

arXiv2011

Resonant Leptogenesis in the Minimal B-L Extended Standard Model at TeV

We investigate the resonant leptogenesis scenario in the minimal B-L extended standard model(SM) with the B-L symmetry breaking at the TeV scale. Through detailed analysis of the Boltzmann equations, we show how much the resultant baryon asymmetry via leptogenesis is enhanced or suppressed, depending on the model parameters, in particular, the neutrino Dirac Yukawa couplings and the TeV-scale Majorana masses of heavy degenerate neutrinos. In order to consider a realistic case, we impose a simple ansatz for the model parameters and analyze the neutrino oscillation parameters and the baryon asymmetry via leptogenesis as a function of only a single CP-phase. We find that for a fixed CP-phase all neutrino oscillation data and the observed baryon asymmetry of the present universe can be simultaneously reproduced.

hep-ph↗

arXiv2011

Stochastic Equations in Black Hole Backgrounds and Non-equilibrium Fluctuation Theorems

We apply the non-equilibrium fluctuation theorems developed in the statistical physics to the thermodynamics of black hole horizons. In particular, we consider a scalar field in a black hole background. The system of the scalar field behaves stochastically due to the absorption of energy into the black hole and emission of the Hawking radiation from the black hole horizon. We derive the stochastic equations, i.e. Langevin and Fokker-Planck equations for a scalar field in a black hole background in the $\hbar \rightarrow 0$ limit with the Hawking temperature $\hbar κ/2 π$ fixed. We consider two cases, one confined in a box with a black hole at the center and the other in contact with a heat bath with temperature different from the Hawking temperature. In the first case, the system eventually becomes equilibrium with the Hawking temperature while in the second case there is an energy flow between the black hole and the heat bath. Applying the fluctuation theorems to these cases, we derive the generalized second law of black hole thermodynamics. In the present paper, we treat the black hole as a constant background geometry. Since the paper is also aimed to connect two different areas of physics, non-equilibrium physics and black holes physics, we include pedagogical reviews on the stochastic approaches to the non-equilibrium fluctuation theorems and some basics of black holes physics.

hep-th↗

arXiv2011

Can we detect "Unruh radiation" in the high intensity lasers?

An accelerated particle sees the Minkowski vacuum as thermally excited, which is called the Unruh effect. Due to an interaction with the thermal bath, the particle moves stochastically like the Brownian motion in a heat bath. It has been discussed that the accelerated charged particle may emit extra radiation (the Unruh radiation) besides the Larmor radiation, and experiments are under planning to detect such radiation by using ultrahigh intensity lasers. There are, however, counterarguments that the radiation is canceled by an interference effect between the vacuum fluctuation and the radiation from the fluctuating motion. In this reports, we review our recent analysis on the issue of the Unruh radiation. In this report, we particularly consider the thermalization of an accelerated particle in the scalar QED, and derive the relaxation time of the thermalization.

hep-ph↗

arXiv2011

Unruh radiation and Interference effect

A uniformly accelerated charged particle feels the vacuum as thermally excited and fluctuates around the classical trajectory. Then we may expect additional radiation besides the Larmor radiation. It is called Unruh radiation. In this report, we review the calculation of the Unruh radiation with an emphasis on the interference effect between the vacuum fluctuation and the radiation from the fluctuating motion. Our calculation is based on a stochastic treatment of the particle under a uniform acceleration. The basics of the stochastic equation are reviewed in another report in the same proceeding. In this report, we mainly discuss the radiation and the interference effect.

hep-ph↗

arXiv2010

Non-Equilibrium Fluctuations of Black Hole Horizons

We investigate non-equilibrium nature of fluctuations of black hole horizons by applying the fluctuation theorems and the Jarzynski equality developed in the non-equilibrium statistical physics. These theorems applied to space-times with black hole horizons lead to the generalized second law of thermodynamics. It is also suggested that the second law should be violated microscopically so as to satisfy the Jarzynski equality.

gr-qc↗